Sensorless Voltage Control of a Three-Phase Grid-Connected Inverter Using an Estimated Synchronous Reference Frame

This paper proposes a sensorless algorithm for phase synchronization in three-phase grid-connected inverters, designed to eliminate the use of voltage sensors. Voltage sensors often raise the system cost and complexity, and are susceptible to electrical noise, which makes sensorless alternatives more attractive for building simple and reliable inverter systems. The proposed method estimates the grid voltage in a synchronous reference frame by applying a model similar to the back electromotive force (EMF) used in permanent magnet synchronous motors (PMSMs). A disturbance observer and the arctangent function are used to calculate the grid phase and frequency, and a proportional-integral (PI) controller is applied to synchronize the inverter phase with the grid. The proposed method is verified through simulation and experimental testing, and the results confirm its feasibility and performance under various conditions.